1. Field of the Invention
The present invention relates to the field of solid rivets.
2. Prior Art
Solid rivets of various kinds are of course very well known in the prior art. Of particular importance to the present invention are solid rivets of the type which are generally used for sealing applications such as, by way of example, may be used in the construction of aircraft wing fuel tanks and the like. In such applications, the rivets are intended not only to join two or more metallic sheets or members, but to also provide a seal for the rivet hole so that there will be no fuel leak around the rivet.
One such sealing rivet was developed for use in fuel sealing applications for the Boeing Aircraft model 727 wing structure. That rivet, identified as the BACR15DG rivet, was intended for use with a workpiece having a bore, a first substantially cylindrical counterbore and a second counterbore which is frustro-conical and tapers forwardly between the first counterbore and the bore. The rivet itself had a head including an endface, a first cylindrical section located forwardly of the endface and a second tapered section forwardly of the first section between the first section and the rivet shank, the tapered section of the rivet substantially matching the taper of the frustro-conical counterbore of the workpiece. The entire endface of the head end of the rivet had a dome shape defined by a predetermined spherical radius of an amount dependent upon the size of the rivet. When the rivet was placed in position in the workpiece and set using a flat or substantially flat tool against the head end of the rivet, the dome shape of the rivet was flattened, substantially expanding the first section of the head into tight fuel-sealing engagement with the first counterbore in the workpiece.
The characteristics of the BACR15DG rivet in comparison to the counterbores in the workpiece before setting the rivet and the characteristics of the rivet after setting are best illustrated by considering the specific dimensions for a specific rivet of the BACR15DG series. By way of example, for the 3/16ths diameter shank rivet, the combined height of the conical section and the cylindrical section of the head range from 0.085 inches to 0.090 inches, with the corresponding dimensions for the hole specification ranging from 0.075 to 0.085 inches. Thus the periphery of the head of the rivet prior to setting would range from flush to 0.015 inches above the surface of the workpiece. The diameter of the first section of the 3/16ths rivet ranges from 0.2700 to 0.2725 inches, with the diameter of the corresponding counterbore in the workpiece ranging from 0.269 to 0.274 inches. Thus the head of the 3/16ths rivet can range from having a 0.002 inch radial clearance to approximately a 0.0018 inch radial interference with the workpiece before setting the rivet. As set, the specification for the unshaven head height for the 3/16ths inch BACR15DG rivet was 0.002 to 0.010 inches. In aerodynamic applications, it is generally required that the head height of a set rivet be in the range of 0.002 inches to 0.005 inches, the upper limit being determined by aerodynamic considerations and the lower limit being determined as assuring that the face of the setting tool "bottomed" on the head of the rivet, not on the workpiece. Given these dimensions and tolerances, it is therefore apparent that statistically most of the 3/16th BACR15DG rivets were probably either slip fit or a lose fit in the counterbore in the workpiece prior to setting. Also, the dimensions of the heads of many of the set rivets would satisfy the head protrusion limits for aerodynamic applications, though clearly many others would require shaving after setting to meet such requirements.
A very similar rivet is disclosed in U.S. Pat. No. 4,000,680 entitled "Expanding Head Riveting Method and System". In that patent a domed head rivet is disclosed wherein the spherical section of the dome extends radially outward to a position short of the periphery of the first or cylindrical section of the head, curving into the otherwise flat endface of the head just outboard of the shank diameter. Also, the cylindrical section of the head is of a diameter less than but about the same as the diameter of the first counterbore to always provide clearance therebetween prior to setting. Subsequent patents to the same inventor, including U.S. Pat. Nos. 4,051,592, 4,086,839 and 4,156,666, related to the foregoing patent, disclose a dome headed rivet having what is referred to as a "ring dome" rather than a central dome, the ring dome being aligned with the outer diameter of the rivet shank. Rivets of this latter type have enjoyed substantial commercial success and are commonly used in fuel sealing aircraft applications wherein the workpiece has a cylindrical counterbore followed by the second frustro-conical counterbore joining the cylindrical counterbore with the bore through the workpiece.
The cylindrical head of the ring domed rivets expands radially on setting of the rivet to tightly engage the cylindrical counterbore in the workpiece when the counterbore is of proper depth, with the head of the set rivet generally being within the limits for aerodynamic usage without shaving of the head. At the same time the conical section of the rivet is generally in firm engagement with the frustro-conical tapered section of the hole in the workpiece, giving the desired strength and fatigue resistance for the set rivet. However sometimes the first counterbore (and thus the tapered section) of the hole in the workpiece is drilled too deeply. In such cases when a ring domed rivet is installed in such a deep counterbore, the periphery of the head remains substantially flush with the top of the workpiece and the head is flattened to at least somewhat radially expand the head so that the resulting installation has substantially the same appearance as a dimensionally correct and properly installed ring domed rivet in a dimensionally correct counterbored hole in the workpiece.
However in the case of the rivet set in the deep counterbore, the rivet becomes forced upward off of the conical portion of the counterbore, leaving a small gap between the tapered portion of the counterbore and the tapered section of the rivet head. This small gap allows the parts to move relative to each other under repetitive stress and vibration, resulting in a loosening of the head and the development of a fuel leak therearound. Accordingly, with these prior art rivets the only way to assure a proper joint is to first assure that the counterbored holes in the workpiece are within specification tolerances to start with by appropriate inspection thereof. The inability to inspect for this condition after the setting of the rivet is a substantial disadvantage however, as there is no opportunity to detect a lack of inspection of the holes or alternatively, an improper inspection thereof, after the ring dome rivets have been set. Accordingly, one of the primary objects of the present invention is to provide an expanding head rivet for fuel sealing and similar applications which can be inspected after the setting of the rivet so as to reveal an excessively deep counterbore as opposed to a proper counterbore, and for that matter to also reveal a shallow counterbore, all in a rivet which when properly installed in a proper counterbore will not require shaving in aerodynamic applications. The same will also occur with the center domed rivets of U.S. Pat. No. 4,000,680, as the dome is almost entirely within the shank diameter.
In addition to the foregoing prior art, also relevant for background purposes are U.S. Pat. Nos. 3,526,032, 3,747,467, 3,927,458, and 4,004,484. Also relevant are the following foreign patents: Russian Patent No. 516,848, German Patent No. 707,103, Russian Patent No. 409,016 and Russian Patent No. 517,709.